IPv4 and IPv6 are two versions of the Internet Protocol. The main difference lies in their address space; IPv4 uses 32-bit addresses, allowing for approximately 4.3 billion unique addresses, while IPv6 employs 128-bit addresses, significantly expanding the potential for unique addresses to about 340 undecillion. Additionally, IPv6 introduces improved security features, auto-configuration capabilities, and better support for multicast connections. As the internet continues to grow, transitioning from IPv4 to IPv6 is essential for accommodating more devices and enhancing network performance.